1275 midget advance curve...

[moggymaniac]

Hi all,
So I got the moggy going with the 1275 spridget engine and type 9 'box - thanks Philthehill for the engine backplate spacer advice; it worked a treat!
Unfortunately it seemed to have more get up and go with the tired 1098cc engine in!

My setup is as follows:

+60" pistons - i believe this makes it a 1330
minisport stage 2 cylinder head - standard minor/midget style rockers (not the fatter square later type rockers)
unsure about cam as I haven't had it out to check casting numbers
LCB exhaust manifold and 1.75" 2 box exhaust system
mini/metro inlet manifold with HIF44 carb ( just rebuilt ) and BDL needle
accuspark 45D electronic distributor - previously used in my 1098cc and transferred but no changes made to mechanical advance

At the MOT they told me it was running slightly lean, and to rebuild the carb, so I did, and I managed to pick up a wideband AEM A/F ratio kit on ebay for just £70 (!!!) which I've fitted so that I can take readings and reprofile my needle to suit the engine etc. I've noticed that it is actually rich when idling so I will adjust that tomorrow on the mixture screw. Sooty plugs indicate I'm slightly rich also, but after a good run yesterday I will whip them out and see what they look like tomorrow. Also if anyone has any idea what A series specific A/F readings I should be looking for at idle, cruise/light load/part throttle and wide open throttle/acceleration/hill climb, please kindly share. From what I've read, I'm aiming for idle 13.4:1 - 14:1, Cruising 14:1 - 14.5:1 (or maybe a tad richer depending on my engine) and Wide open throttle 12:1 - 12.5:1.

The main issues are general lack of power, and on motorway cruising she seems ok but then occasionally has a momentary heavy single misfire/cough back through the carb (this is what it sounds like anyway) every 5 minutes or something.

The MOT station guy said to remove the vacuum advance and plug it, which I've done. Not pleased with results and have since read that I should have it connected to get a better advance curve for my engine.

Which got me thinking...the Accuspark 45D Elctronic distributor fitted may have the wrong primary and secondary spring fitted, providing the wrong amount of advance. It also has issues of kicking back (trouble turning over, like it is catching) when I try to start the car, which as I've read points to being too advanced at static???

She also nearly stalled after revving the car when returning to idle, which I think is worse since removing the vacuum pipe.

I'm going to do a compression test tomorrow, check for any intake leaks, earth connections, recheck rocker and plug gaps, reconnect vacuum pipe, and once having a play around with the needle profile to optimise fuelling, maybe retard the distributor slightly. With regards to fuelling, i have one of those solid state fuel pumps off ebay which looks like an SU but doesn't use points. Never had any issues on the 1098 but maybe it isn't up to the demands of my new setup. I just don't know.

Maybe once I've got the fuelling right I can take the distributor to AC Dodd and get him to sort out the mechanical advance for me by setting up the dizzy.

Could poor timing give me erroneous A/F ratio readings?

This thread is me thinking out loud as a relatively inexperienced minor owner, so any wisdom and thoughts are very welcome!

J

[Mark Wilson]

I can't offer a great deal of advice here as you seem to be far ahead of me in your knowledge, and my rebuild won't be tested for a few months yet. However, I did go through something of the same process when selecting a dizzy for my Midget 1275 (12CE) and having spoken to Martin Jay (Distributor Doctor) decided that the Accuspark was unlikely to have the "correct" advance curve. He recommended fitting a reconditioned 25D 41270, but his prices were a bit high for a bread and butter Traveller, so I found a decent looking used one on eBay, changed the vacuum advance and the springs and fitted an Accuspark unit. As I said, not tested yet.

The table in the link below shows the differences in the advance curves between the 41270 for the 1275 and the 41269 for the Minor 1098 (handily on adjacent rows!). I don't think the 1098 ever had a 45D so no info for that.

http://www.sterlingbritishmotoringsocie ... _Chart.pdf

Mark

[Monty-4]

Your cruising misfire sounds exactly like the lean misfire I had with a HiF38 due to the cruising economy connection. Temporarily blanking off that connection, and then later fitting a richer needle solved that one.

I'm going through the same thing as you, tuning in a new engine, albeit of a very different spec. If you work out what the cam is you can take a good guess at the advance curve (the Aldon 'Yellow' is reported to suit many engines of mild tune but not cheap) and then play with needles for a while. Otherwise to truly nail the tune an expensive rolling road session is going to be required. Or perhaps a passenger with your A/F ratio gauge if it could be used while driving!

[IslipMinor]

A number of thoughts here:

Vacuum advance is a GOOD thing, particularly at around town type speeds. I forgot to reconnect ours a few years ago and immediately found that the urban driving was worse.

Mixture needs to be a tad 'rich' under load, and apart from on a very light throttle, not 'lean'. The engine is not designed to run lean, and the exhaust valves will hate it!

Static timing - max of 10° BTDC 'static', and then a max of 20° centrifugal advance (10° distributor) advance, giving a maximum total of 30° centrifugal advance - the vacuum will be on top of that, but only comes in on light throttle openings.

Depending on the cam spec, I would have expected at least 80bhp at the flywheel from the spec you describe, which will give you a good 'spirited' performance.

It would be worth a rolling road session to sort it out.

[moggymaniac]

Thanks for the replies! V interesting!

I had a playground with mixture at idle and took her for a good run yesterday with vacuum reconnected. Definitely helps smoothness especially between gear changes and under light load.

Got back and the plugs were a healthier colour. My A/F gauge tells me that it is lean in the mid range, but a little rich on idle and wide open throttle. Raised the jet slightly in mind of evening out top and bottom ends before I attempt to file down my needle.

Did a compression test warm when I returned, and have 150 on all for cylinders dry and 155 on all cylinders wet. While it isn't the strongest compression, at least the rings/cylinders appear not to be worn from the wet test results. I should say I bought this engine as a used unit having done 14000 miles since rebuild.

I thought I would check for leaks around the inlet manifold next and sprayed some brake cleaner around the area...hey presto! A big leak at the front of the manifold causing the engine to nearly stall. I will take off and add some instant gasket to see if that stops it. Otherwise I fear the metro inlet manifold is warped and will require a skim.

At least I have some sort of diagnosis for now which will be contributing to lack of power!

I would love some sort of 3D ignition kit like a 123 distributor so that I can plot the near best advance curve and experiment without the cost of a rolling road (and learn about tuning in the process!!). This is unfortunately out of my price range, so I will sort the intake leak, get the mixture correct and keep adjusting the dizzy for the best results, and then pop the dizzy out and have apart to see what sort of mechanical advance I have as I believe it should be printed on the bottom plate in degrees? I don't know much yet about distributors, but my vacuum advance unit body is a little loose on the distributor. It may have a nut on the inside of the dizzy body which I can tighten. Not sure if this would affect the curve also.

Will do some more when I get a chance and report back.

Thanks so far for the advice!

[IslipMinor]

it should be printed on the bottom plate in degrees?

Yes, it should and will be in 'distributor' degrees, and would normally be around 10/12° or 20/24° 'crankshaft'. If it is more, then the static °BTDC will need to be reduced, to maintain a total of 30/32° 'crankshaft', BUT this will affect the low speed running. The standard distributor uses less 'static' and more 'centrifugal' than is used today, mainly because at 95 Octane, the lowest level fuel quality available today, allows more low speed ignition advance than the fuel quality available at the time the A-Series engine was designed. 'Premium' fuel was around 80/85 Octane!

[moggymaniac]

Good to know!
I'm wondering how accuspark can advertise their electronic 45d distributors in a 'fits many vehicles' fashion, when these engines differ and all have different mechanical and centrifugal advance requirements?

[moggymaniac]

Looking at the chart that mark posted above, it must have the wrong curve. I do have the original 25d side entry distributor that came with the 1275 engine. Perhaps I could use the springs and weights from this while utilising the rest of the accuspark 45d parts to get a 'normal' midget curve?

[midget]

My advice , for what it's worth, is to (as you intimated) take it to a GOOD rolling road guy. I did this with my modded 1098 and the result was absolutely stunning. The first thing he did was throw my electronic ignition stuff in the bin,along with the modern coil.
If you are willing to travel, pm me and I'll send his details. BTW he 'aint cheap but looks after many successful competition cars.

[Mark Wilson]

Good to know!
I'm wondering how accuspark can advertise their electronic 45d distributors in a 'fits many vehicles' fashion, when these engines differ and all have different mechanical and centrifugal advance requirements?

They will probably perform significantly better than a "correct" dizzy with worn springs and seized weights and vac unit, particularly if the car is used only for gentle summer runs. The precision of the advance curves probably only really matters for those owners with competition ambitions, or for correctness obsessives like me

[Declan_Burns]

I suggest you read through this-it has all the info you may need.
http://www.mg-cars.net/mg-midget-sprite ... 120585.htm

Regards
Declan

[philthehill]

Unfortunately once you stray from standard original build spec the manufactures standard advance curves are irrelevant to the modified engine spec.
However close to the original manufactures advance curve you get it will never be right. The distributer should be re-worked or replaced with one that matches the revised engine spec & which can only be done using either a rolling road or engine dynometers. Without utilising either of those machines the timing and advance will be at best a guesstimate.
Phil

[moggymaniac]

I have had the inlet manifold skimmed, binned the jonspeed 'competition' manifold gasket which leaked still and have fixed the intake leak by fitting a minisport standard gasket. haven't got round to needle reprofiling yet, but I may take this to AC Dodd and get a pro to do it for me (if I can get his details...)

I have the opportunity to buy a 123 midget distributor 9(used - 1000 miles) with 16 preset curves as follows:

Curve (switch setting) //Advance@500-1000 rpm // advance@ 2000 rpm* //maximum@ 5000 rpm*
0 10,0 14,5 28
1 10,0 16,7 28
2 10,0 18,4 28
3 10,0 20,2 28

4 10,0 16,3 30
5 10,0 17,6 30
6 10,0 19,4 30
7 10,0 21,1 30

8 10,0 16,2 32
9 10,0 18,1 32
A 10,0 20,3 32
B 10,0 22,9 32

C 10,0 17,0 34
D 10,0 20,4 34
E 10,0 22,1 34
F 10,0 23,9 34
* degrees advance and engine speed both relate to the crankshaft

vacuum-advance 0 to 14 degrees from 5 to 10 inch Hg

My question is, for my setup as listed at the top of this thread, am I likely to find the right curve from the figures above? Or should I just buy a 123 TUNE with fully programmable curve, then get it to a rolling road? Thinking of saving the pennies here, but it may not be worth it...

[philthehill]

I am glad to hear that you have sorted the original problem(s).
My preference would be to purchase the 123 Midget distributer 9 and then you have 16 chances of getting it right.
By road testing the car and varying the distributer settings you have a very good chance of getting it right without incurring the expense of putting the car on a rolling road.
Phil

[BrianHawley]

I am glad to hear that you have sorted the original problem(s).
My preference would be to purchase the 123 Midget distributer 9 and then you have 16 chances of getting it right.
By road testing the car and varying the distributer settings you have a very good chance of getting it right without incurring the expense of putting the car on a rolling road.
Phil

What are rolling road fees like these days Phil?

[philthehill]

Brian
I would expect to pay between £200 and £350 dependent upon the size of the car and what needs to be done to it.
Here is a link to a rolling road local to me with specified approx. costs.
http://www.aireytuning.com/

Phil

[BrianHawley]

Brian
I would expect to pay between £200 and £350 dependent upon the size of the car and what needs to be done to it.
Here is a link to a rolling road local to me with specified approx. costs.
http://www.aireytuning.com/

Phil

Many thanks, much appreciated.

[Admin]

What are rolling road fees like these days Phil?

I've used Southam Mini Metro Centre a couple of times who tune A Series lumps for racing. Last summer they were in the order of £230 if memory serves me correct, took them about two, maybe two and a half, hours work on the car. Impressed with the results.

[liammonty]

If second that - I used Southam Mini and Metro Centre and the results were very good. It will cost you less than a 123 distributor will

[moggymaniac]

Did this include the price of changing distributor springs etc? Otherwise I need a new distributor anyway...thinking that a fully programmable curve is best of taking to a rolling road...?